Conventional light stability testing devices will be described with reference to FIG. 8, FIG. 9, FIG. 10, and FIG. 11.
FIG. 8 is a front view showing the main part of a first light stability testing device according to a prior art. This light stability testing device 1 regulates light rays emitted from a light source 2 by an optical system 3, irradiates the same onto a sample (unillustrated) placed on a sample stage, thereby testing light stability of the sample. The optical system 3 is composed mainly of a first reflecting mirror 31, a light regulating means 33, an integrated lens 35 as a light flux control means, a second reflecting mirror 37, and a third reflecting mirror 39. For the integrated lens 35, chalk-like quartz sticks are bundled and a spherical glass is adhered to the top. When light rays pass therethrough, each quartz column behaves like a small light source. Thereby, even if, for example, a light flux after passing through an appointed diaphragm is rectangular, this light flux can be changed to a circular light flux.
4 denotes a sample stage for placement of a sample (unillustrated), and to this sample stage 4, a visible light measuring sensor 5 for measuring the dose of visible light and an ultraviolet measuring sensor 6 for measuring the dose of ultraviolet rays are attached. Herein, the sample stage 4 is rotatable by driving force of a drive unit 7 via a rotation axis 71.
This first light stability testing device 1 according to the prior art is divided broadly into a lamp house 8 and a sample chamber 9, and in the above-described construction, the light source 2 and the first reflecting mirror 31, light regulating means 33, integrated lens 35 as a light flux control means 35, and second reflecting mirror 37 of the optical system 3 are installed in the lamp house 8, while the third reflecting mirror 39 and sample stage 4 of the optical system 3 are installed in the sample chamber 9.
FIG. 9 shows a first light stability testing device 1 having the above-described construction in detail. Namely, the light regulating means 33 included in the optical system 3 comprises a diaphragm as a total light regulating means 331 and an ultraviolet limit filter as an ultraviolet regulating means 333. The diaphragm as a total light regulating means 331 uniformly regulates and controls the quantity of all light rays of visible light and ultraviolet rays, and the ultraviolet limit filter as an ultraviolet regulating means 333 controls only ultraviolet rays (in particular, far ultraviolet rays) of light rays. 91 denotes an entrance window made of quartz glass, which is provided for the sample chamber 9. Herein, as the light source 2, a xenon lamp is used.
In the first light stability testing device 1 having the above-described construction, first, a sample (unillustrated) is placed on the sample stage 4. Then, light rays are emitted from the xenon lamp of the light source 2. These light rays are first converged by the first reflecting mirror 31, and then pass through the ultraviolet limit filter as an ultraviolet regulating means 333 for control of ultraviolet rays. Then, the light rays are passed through the diaphragm as a total light regulating means 331 for regulation and control of the total quantity of light, that is, the quantity of all light rays of visible light and ultraviolet rays. Then, the light ray direction is regulated by the integrated lens 35 as a light flux control means. Then, the light ray direction is changed to approximately horizontal, and the light rays enter the sample chamber 9 through the quartz glass entrance window 91, and furthermore, the light rays are reflected downward by the third reflecting means 39 and irradiated onto a sample (unillustrated) placed on the sample stage 4. Since irradiation is carried out for a long time, for an improvement in irradiation distribution, the sample stage 4 is rotated by the drive unit 7 via the rotation axis 71 during the irradiation, whereby light stability of the sample is tested.
In addition, during the above-described irradiation, a signal from either visible light measuring sensor 5 or ultraviolet measuring sensor 6 is transmitted to a control unit (unillustrated), and based on computing by this control unit, the quantity of light rays and time are controlled.
On the other hand, FIG. 10 is a front view showing a main part of a second light stability testing device according to a prior art. Unlike the above-described first light stability testing device, this second light stability testing device 1 uses fluorescent lamp-like tubular light sources as light sources 2, has no large scale optical system, and simply has a reflecting mirror 31. In other words, in this second light stability testing device 1, light rays emitted from the light sources 2 are directly irradiated onto a sample. 333 denotes a stationary ultraviolet regulating means, which is for regulation of the quantity of ultraviolet rays from the light sources.
5 denotes a visible light measuring sensor, 6 denotes an ultraviolet measuring sensor, and these are attached to a sample stage 4. The sample stage 4 is rotatable by driving force of a drive unit 7 via a rotation axis 71.
During irradiation, the quantity of light from the light sources 2 are regulated based on a signal from the visible light measuring sensor 5. In addition, values measured by the ultraviolet measuring sensor 6 are integrated and recorded.
However, in the above-described light stability testing devices 1 according to the prior arts, the following problems have existed.
FIG. 11 is a diagram showing spectrum distributions of sunlight, a xenon lamp, and a D65 lamp (TOSHIBA FLR20S and DEDL-D65/M). The horizontal axis indicates a wavelength, and the longitudinal axis indicates a relative value of intensity. As shown in FIG. 11, spectrum distributions of light sources which approximate sunlight, such as, a xenon lamp and a D65 lamp have excessive ultraviolet parts compared to the spectrum distribution of sunlight. In general, visible light is in a range of 380 nm to 780 nm and is visible to human eyesight. Ultraviolet rays have a wavelength from 200 nm to 380 nm and are, therefore, invisible to the naked eye. Strictly, this wavelength range is called a near-ultraviolet range, and a range from 100 nm to 200 nm is called a far-ultraviolet range (Toshiharu Tako, Junpei Tsujiuchi, Shigeo Minami (eds.), “Light Measurement Handbook,” 2nd ed. published Jan. 20, 1997, p. 572).
On the other hand, criteria of the Ministry of Welfare for a light stability test of a drug, etc., of a sample have been provided based on sunlight, and concretely, an integrated dose has been provided as 1200 kLxhr or more for visible light, and for ultraviolet rays, as 200 whr/m2 or more.
Accordingly, in the light stability testing unit 1 according to the prior art, with respect to the light source 2 having excessive ultraviolet rays such as a xenon lump, the ultraviolet limit filter as an ultraviolet regulating means 333 is a stationary type and sets the quantity of ultraviolet rays to approximately the above-described prescribed value.
However, a light stability test extends for a long time, and for example, if an instantaneous irradiation value of 1000 Lx is selected, it extends for no less than 1200 hours. Accordingly, a deterioration in the light source 2 and the optical system 3 occurs with an elapse of time. Moreover, this tendency to deteriorate is greater in the ultraviolet part than in the visible light part, therefore, if a light-reducing value of the ultraviolet limit filter as the ultraviolet regulating means 333 has been designed for the lowest dose, ultraviolet rays are likely to become insufficient when visible light reaches 1200 kLxhr, and as a result, an accurate light stability test cannot be conducted, therein a problem exists.
On the other hand, in the aforementioned second light stability testing device, deteriorating tendencies of the light sources 2, etc., are different among the plurality of light sources 2 and cannot be easily estimated. Accordingly, the dose is usually set to a slightly excessive dose, and when the integrated dose of visible light reaches 1200 kLxhr, ultraviolet rays may reach 220-280 whr/m2 if the light sources 2 are new. In actuality, in terms of a sample such as a drug, an influence of ultraviolet rays thereon is often greater, and as a result, an accurate light stability test cannot be conducted, therein a problem exists.
Therefore, the present invention has been made to solve the above-described problems and an object thereof is to provide a light stability testing device which enables an accurate ultraviolet irradiation and an accurate visible light irradiation, and thus can conduct an accurate light stability test.